Coil assemblies for electric machinery and apparatuses and communication machinery and apparatus have heretofore been prepared by winding an insulated wire into a desired shape, and thereafter varnishing it to cause mutual adhesion of the wire and solidification thereof. Recently, however, self-bonding insulated wires which can be mutually fusion-bonded only by heating or solvent treatment have come to be used in place of the conventional varnish impregnated wires.
The self-bonding insulated wire has a self-fusion-bonding layer composed mainly of a thermoplastic resin provided on an insulation layer of an enameled wire. From this wire, a coil is prepared by winding the wire into a coil shape and heat-treating or solvent-treating it during or after the winding to cause mutual adhesion of the wire, so that the varnish-impregnation treatment can be omitted, which results in the advantages as below:
(1) Pollution problems, and safety and hygiene problems which may be caused by use of an impregnation varnish are eliminated.
(2) Production cost can be reduced because the coil producing process is simplified and shortened by using no impregnation varnish but current-flow heating, for example.
(3) A coil which has a complicated shape or which does not allow penetration of varnish can be solidified.
Accordingly, with the increasing demand for self-bonding insulated wires, new materials therefor are desired which have various characteristics to meet production processes and the desired conditions of use. In particular, deflecting yoke coils which are used for televisions, etc., are subjected to various severe requirements by users and coil manufacturers because of the special shape and necessary strict dimensional accuracy of the coils.
Several years ago, coil manufactures changed the self-fusion-bonding material from a polyvinyl butyral to a polyamide copolymer resin to meet the requirements of low thermal deformation, high bonding strength at elevated temperatures (e.g. about 100.degree. C.), and high flowability of the self-fusion bonding materials during the current-flow heat treatment which requirements came to be posed as a result of an increase of the deflection angles of television tubes.
Recently, higher precision CRT's have been demanded with the development of computers, which has led to the requirement for a further reduction of the deformation of deflecting yoke coils. Although the current polyamide copolymers used as self-fusion-bonding insulation materials exhibit a satisfactory bonding strength at an elevated temperature and adequate flowability, the materials per se are soft, so that a yoke coil prepared by using such polyamide copolymer self-bonding insulated wire has disadvantage in that the coil may be somewhat deformed by the spring-back force of the coil after the coil has been produced. Such deformation has become a problem with present high precision CRT's.
On the other hand, self-bonding insulated wires which employ a phenoxy resin as the self-fusion-bonding material are known. Such wires can give deflecting yoke coils exhibiting less deformation. However, the phenoxy resins are deficient in flowability at the heat treatment, so that they require a more intense electric current for current-flow fusion, or longer time of current flow for current-flow fusion in comparison with the conventional polyamide copolymers in order to prepare a coil with mutual wire bonding, which requires more heat energy and results in a rise of the production cost.
Furthermore, intense current flow for a long time disadvantageously causes thermal deterioration or short circuit of the wire.
The present inventors made comprehensive investigation to eliminate the above-mentioned disadvantages, and found the self-bonding insulated wire of the present invention which comprises a material having sufficient flowability similar to conventional polyamide copolymers and which enables the production of deflection yoke coils exhibiting low deformation after fabrication.
Recently, electric machines and apparatus have been more and more miniaturized, and higher reliability is required therefor; additionally, a reduction of the production cost is simultaneously desired.